This relates generally to imaging systems and, more particularly, to imaging systems having interconnects in an image sensor cover layer.
Modern electronic devices such as cellular telephones, cameras, and computers often use digital image sensors. Imagers (i.e., image sensors) often include a two-dimensional array of image sensing pixels. Each pixel typically includes a photosensitive element such as a photodiode that receives incident photons (light) and converts the photons into electrical signals.
In a typical arrangement, an image sensor die includes an image integrated circuit formed on a front surface of the image sensor die and electrical contacts (e.g., a grid of solder balls) formed on a rear surface of the image sensor die. Through-silicon vias are used to electrically connect the image sensor integrated circuit on the front surface of the image sensor die to the electrical contacts on the rear surface of the image sensor die. The image sensor die is then mechanically and electrically coupled to a printed circuit board by soldering the electrical contacts on the rear surface of the image sensor die to the printed circuit board.
There are a number of disadvantages associated with this type of packaging arrangement. The presence of solder balls between the image sensor die and the printed circuit board can lead to unpredictable variations in the distance between the surface of the printed circuit board and the image sensor integrated circuit. The use of through-silicon vias also requires the image sensor die to be thinned to accommodate the through-silicon vias. Excessive thinning of the image sensor die can lead to warping and reliability issues.
It would therefore be desirable to provide improved ways of forming interconnects in image sensors.